gitify: Setup pre-commit hook

Automatically setup pre-commit hook on new installations (if gitify is called with "--hooks). The hook validates that PHP files are well-formed using "php -l".

To update existing installations, simply rerun gitify with the original arguments.

This includes stubs for some other hooks. For more description of available git hooks, see http://git-scm.com/book/en/Customizing-Git-Git-Hooks